With the increasing recording density of magnetic disks, the distance between a magnetic disk serving as a recording medium and a head for recording and reproducing information has become almost nil as they approach coming into contact with each other. The magnetic disk surface is provided with a carbon protective film and a lubricant film (lubricant layer) to diminish abrasion caused by contact with the head or sliding of the head thereon, and to prevent contamination of the disk surface. Specifically, these two layers protect the surface of the magnetic disk. In particular, the lubricant layer provided on the top must have various properties, such as long-term stability, chemical resistance, friction properties, and heat resistance, and fluoropolyethers have been often used as a lubricant for magnetic disks (e.g., Patent Literature 1 and 2).
Recent years have seen the development of a technique called “heat-assisted magnetic recording” (HAMR), which aims to increase the recording density of magnetic disks. In HAMR, a recording spot is heated by laser irradiation immediately before writing. The heating temperature reaches 300° C. or more, and the lubricant on the magnetic disk is exposed to high heat. This evaporate, and the lubricity may not be maintained.
To prevent the evaporation of the lubricant at high temperatures, it is important to enhance the adsorption of the lubricant to the surface of magnetic disks. Patent Literature 3 and 4, for example, have proposed techniques to increase sites for adsorption to the magnetic disk by introducing hydroxyl groups into the molecule. However, these techniques are also still unsatisfactory in the bonds between the lubricant and the magnetic disk, and lubricants capable of forming stronger bonds with magnetic disks have been desired.